The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the inventors hereof, to the extent the work is described in this background section, as well as aspects of the description that does not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted to be prior art against the present disclosure.
Discrete multitone modulation is widely used in digital television and audio broadcasting, digital subscriber line (DSL) Internet access, wireless networks, powerline networks, and 4G mobile communications. In a DMT system, incoming data is collected and then distributed over a large number of small individual carriers, each of which uses a form of quadrature amplitude modulation (QAM) modulation. A DMT transmitter usually includes a forward-error correction encoder that encodes all data to be transmitted into encoded bits before mapping the encoded bits into the subcarriers. After tone mapping, a constellation encoder is then used to distribute the encoded bits into a selected constellation. Then, an OFDM modulator is used to modulate data symbols from the constellation into OFDM symbols.
At a DMT receiver, a constellation decoder is usually used to decode received data symbols. FEC decoders are used to decode the recovered encoded data symbols from the received data symbols. When the throughput of the system is high, e.g., 10 gigabits per second (Gbps), the implementation of FEC decoder is challenging. Specifically, hardware requirements for an iterative decoder such as low-density parity check (LDPC) decoders are difficult to satisfy, because the required circuit area of the decoder increases linearly when the throughput grows.
In addition, the FEC encoding/decoding scheme usually achieves a limited coding rate. In a G.hn network, for example, the mother code of the adopted LDPC has a higher code rate of 5/6, i.e., for every five bits of useful information, the FEC encoder generates a total six bits of data. However, when a higher code rate such as 16/18 or 20/21 is desired, the decoding becomes less efficient because the burden to the FEC decoder increases significantly.